Ducted fan air-vehicles, such as an Unmanned Aerial Vehicle (UAV), may have at least one ducted fan and a fan engine to drive the fan blades. Ducted fan air-vehicles are well-known for performance capability in multiple flight conditions. For instance, ducted fan air-vehicles have the ability of forward flight and are well known for stationary hovering aerodynamic performance.
UAVs are remotely piloted or self-piloted aircraft that can carry cameras, sensors, communications equipment, or other payloads. A UAV is capable of controlled, sustained, level flight and is powered by either a jet or an engine. The UAVs may be remotely controlled or may fly autonomously based on pre-programmed flight plans or more complex dynamic automation systems.
UAVs have become increasingly used for various applications where the use of manned flight vehicles is not appropriate or is not feasible. Such applications may include military situations, such as surveillance, reconnaissance, target acquisition, data acquisition, communications relay, decoy, harassment, or supply flights. These vehicles are also used in a growing number of civilian applications, such as firefighting when a human observer would be at risk, police observation of civil disturbances or crime scenes, reconnaissance support in natural disasters, and scientific research, such as collecting data from within a hurricane.
Currently, a wide variety of UAV shapes, sizes, and configurations exist. Typically it is the payload of the aircraft that is the desired product, not the aircraft itself. A payload is what the aircraft is carrying. UAVs are the delivery system for a payload and are developed to fill a particular application and a set of requirements. As previously mentioned, there are numerous applications for which a UAV may be used. For each new application, a different type of payload may be used. Because different payloads may require different processing capabilities, or may comprise different sizes, a variation of the UAV typically must be developed for each type of payload, or a completely new aircraft typically must be designed. Designing a new aircraft or developing a variation of the current UAV in use is time-consuming and costly.
FIG. 1 is a pictorial representation of a typical ducted fan air-vehicle 100. The ducted fan air-vehicle 100 includes an air duct 102 having a fan 104 located within the air duct 102. The ducted fan air-vehicle may have a center body 106. The center body 106 may be a housing that contains other components of the air-vehicle 100, such as an engine 107 for powering the air-vehicle 100, a camera, or additional components for air-vehicle operation, such as an avionics system 109. The ducted fan air-vehicle 100 may also include a duct pod 113.
The ducted fan air-vehicle 100 may also include a stator assembly 110 and a plurality of fixed and/or movable vanes 112 for providing thrust vectoring for the air-vehicle 100. The stator assembly 110 and vanes 112 may be located downstream or under the fan 104 located within the air duct 102. The stator assembly 110 may be located just under the fan 104 in the air duct 102 to reduce or eliminate the swirl and torque produced by the fan 104. The vanes 112 may also be placed under the fan 104. For instance, the vanes 112 may be placed slightly below an exit section of the air duct 102. The vanes may also include moveable flap surfaces 114.
The ducted fan-air vehicle 100 may further include engine mounts 111 which support the center body 106. Engine mounts 111 also provide a connection for the landing gear 108 of the UAV.
In order to be effective and controllable in multiple flight conditions, ducted fan air-vehicles such as air-vehicle 100 preferably have clean and attached air flow around the duct lip in the multiple flight conditions. Further, ducted fan air-vehicles preferably have a favorable center of gravity in order to be effective and controllable. A uniform inflow velocity profile into the fan is also desirable to minimize the acoustic signature of the duct-fan interaction.
Additionally, ducted fan air-vehicles may need to carry a variety of components when in operation. For instance, in operation ducted fan air-vehicles may need to carry, without limitation, visual sensors, infrared sensors, cameras, radio communication devices, inertial sensor units, ground level sensor units, and/or payload. Due to the limited size of the ducted fan air-vehicle, in order to store the variety of units in the ducted fan, the units may be placed in external pods that are attached to the ducted fan air-vehicle. These pods may (i) cause a shift in the center of gravity, (ii) create negative interference with airflow characteristics inside the duct by blocking air intake and exhaust, and (iii) create additional drag on the UAV when the UAV is in forward flight. Additionally, the added weight of the equipment may require additional engine capacity and fuel storage capacity. It may be beneficial to increase the volume within the duct lip in order to decrease or eliminate the need for external pods while maintaining the aerodynamic requirements of a ducted fan air-vehicle.
Traditional multi-airfoil element control vane sets on ducted fans usually operate in tandem, or together, and may be operated by only one servo. However, if designed such that each vane is independently controlled, the vane pairs may be operated in an opposed fashion—that is they can be deflected towards each other to generate drag and hence generate moments and/or help trim vehicle thrust to enable better control of the ducted fan vehicle. Thus, it would be desirable to design a ducted fan vehicle in which each control vane is operated by its own servo.